1. Field of the Invention
This invention relates to a process of producing an alkenylphenol polymer, and, more particularly, to a process of producing a high molecular weight alkenylphenol polymer at high yield by performing the cationic polymerization of an alkenylphenol in a homogeneous reaction system.
2. Description of the Prior Art
Various studies have hitherto been reported on the production of an alkenylphenol polymer by the radical polymerization of an alkenylphenol, such as p-vinylphenol. However, the products in accordance with conventional methods have a low molecular weight. Therefore, in order to synthesize a high molecular weight polymer, complicated and uneconomical steps were inevitably required. That is, a phenolic hydroxyl group in the molecule of the starting material must first be acetylated (e.g., by converting p-vinylphenol to p-acetoxystyrene) and then subjected to radical polymerization, followed by hydrolyzing the resulting high molecular weight polymer.
Recently, it was reported in Journal of Polymer Science A-1, Vol. 7, p 2405-2410, 1960, that each of the o-, m- and p-isomers of vinylphenol can be subjected to cationic polymerization in the presence of a halogenated hydrocarbon solvent, such as methylene chloride, ethyl chloride, etc., using a cationic polymerization initiator in a non-homogeneous reaction system to obtain the corresponding polymer of high molecular weight. This method was considered as an industrially epoch-making synthesis in the art since a high molecular weight vinylphenol polymer could be synthesized directly from vinylphenol in only one step.
However, this method has several serious defects. One is that the solubility of the alkenylphenol in halogenated hydrocarbons is low, particularly, the solubility remarkably drops at lower temperatures. As is well known in the art, in cationic polymerization the lower the reaction temperature the higher the molecular weight of the resulting polymer. Thus, it is preferred that the alkenylphenol be polymerized at a monomer concentration (i.e., concentration of alkenylphenol in the halogenated hydrocarbon) as high as possible and at a temperature as low as possible. However, in the case that a halogenated hydrocarbon solvent is used, the above demands cannot be satisfied due to limitations on the solubility of the alkenylphenol in the halogenated hydrocarbon solvent. Further, it is not advantageous to use a large quantity of halogenated hydrocarbon solvent, and, also, cost increases are inevitable with increased size of the reaction apparatus used. Another defect of this method is that the stability of the alkenylphenol in the halogenated hydrocarbon solvent is not satisfactory. As a result, a substantial amount of polymer is formed at room temperature even in the absence of the polymerization initiator, which results in introducing a loss of the starting material monomer. Still further, this method provides a polymerization reaction of poor reproducibility so that a low molecular weight polymer is often unexpectedly formed though a high molecular weight polymer having a molecular weight of about 200,000 can be produced at low temperature (-20.degree. C.) even under the same reaction conditions.